This disclosure relates to the production of low density polyurethane foam with low or no amine emissions, particularly full water blown spray polyurethane foams.
The primary use of spray foam is in commercial and residential areas where spraying polyurethane foam brings advantages such as heat and sound insulation as well as mechanical integrity for the structures and surfaces in contact with spray foam material. Typically polyurethane foam is made by reacting isocyanate or polyisocyanate with a polyhydroxyl compound in the presence of certain additives such as surfactants, catalysts, crosslinkers and blowing agents.
Blowing agents are typically low boiling point liquids that can vaporize when heat is generated during the reaction of isocyanates with polyols and crosslinkers. Thus, density can be controlled to some extend by the amount of blowing agent present in the polyurethane formulation. In the past, chlorofluorocarbons (CFCs) were used as effective blowing agents but in recent years their use has been banned due to environmental concerns related to stratospheric ozone depletion. Replacing CFCs with other blowing agents is an ongoing challenge. After the phase out of CFCs other blowing agents were developed including hydrochlorofluorocarbons (HCFCs) as an interim solution. HCFCs are substances that still contain chlorine however their ozone depletion potential (ODP) is lower than those of CFCs due to their shorter life in the environment. Some other alternatives are now currently available or under development. For example CFCs can be conveniently replaced by hydrofluorocarbons (HFCs) which have lower ODP than CFCs. Another alternatives include HFO (hydrofluoroolefins), FO (fluoroolefins), CFO (chlorofluoroolefins) and HCFO (hydrochlorofluoroolefins) all of which are characterized in having low life in the environment resulting in low ODP as well as low GWP. Examples include trans-1,3,3,3-tetrafluoroprop-1-ene or HFO-1234ze; tran-1-chloro-3,3,3-trifluoropropene or HCFO-1233zd; 2,3,3,3-tetrafluoropropene or HFO-1234yf, mixtures thereof and similar structures. However, these blowing agents are relatively expensive when compared with other available materials such as acetone or carbon dioxide. The most convenient route for blowing polyurethane polymers is by in-situ generation of carbon dioxide when isocyanates react with water.
However, obtaining low density polyurethane foam using water as the main or sole blowing agent requires isocyanate to react with a substantial amount of water and this process needs to be catalyzed by suitable amine catalysts. Amines such as bis-(dimethylaminoethyl)ether (BDMAEE) or pentamethyl-diethylenetriamine (PMDETA) are the standard catalysts used to make low densities foam (0.5 lb/cubic feet) with water as the blowing agent.
BDMAEE and PMDETA are characterized by their high vapor pressure and strong amine odor. Thus, amine exposure can occur during system preparation (blending of formulation components), spraying (application) and final use (occupancy).
BDMAEE is generally considered the most efficient catalyst available to activate water towards isocyanate and it is expected that any combination of catalysts containing isocyanate reactive groups would be less effective than BDMAEE. The reason for the superior performance of BDMAEE has been attributed to the N—C2-O—C2-N molecular backbone which has the ideal geometry for water activation. The reactivity of conventional catalysts is discussed in “The Influence of Tertiary Amine Structure on Blow-To-Gel Selectivity” by M. L. Listeman et al., Polyurethanes World Congress, 1993.
GB 0966338 relates to polyurethane lacquers and surface coatings and the use of aliphatic isocyanate derivates, certain metallic compounds or amines in preparing such polyurethane lacquers and surface coatings. GB 1063508 discloses the preparation of rigid foamed polyurethane in situ on a surface. GB 1064555 relates to the preparation of rigid polyurethane foams having improved physical properties. U.S. Pat. No. 3,202,631 discloses a process for stabilizing polyurethane elastomers within a Mooney plasticity range suitable for processing on a mill. More particularly, it discloses a method for preventing the un-controlled post curing of a polyurethane elastomer. U.S. Pat. No. 3,645,924 describes processes for preparing aliphatic-isocyanate based open-cell flexible foam and polyurethane moisture-cure coatings. U.S. Pat. No. 3,740,377 concerns a one-step process for preparing polyurethane-urea resins and elastomers. US 2010/0099785 provides methods and compositions for forming a catalyst. In one aspect, the catalyst is formed by mixing at least one tertiary amine with at least one polymer acid. Such catalysts are particularly useful in the polymerization of polyurethane foams.
The disclosure of the previously identified references is hereby incorporated by reference